<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            display: flex;
            width: 60%;
            height: 300px;
            margin: 100px auto;
            background-color: skyblue;
        }
        span{
            width: 100px;
            height: 100px;
            background-color: slateblue;
        }
        span:nth-child(2){
            /* 控制排列顺序数值越小越靠前默认数值为0 */
            order: -1;
        }
        span:nth-child(3){
            /* 控制子项自己在侧轴的排列方式 */
            align-self: center;
        }
    </style>
</head>
<body>
    <div>
        <span>1</span><span>2</span><span>3</span>
    </div>
</body>
</html>